It is common to provide medical devices designed to be implanted in the vasculature of a patient with one or more barbs for securing the medical device in position within the vessel and for ensuring that the medical device does not migrate over time. The barbs are typically pin-like elements which are able to penetrate into the tissue of the wall of the vessel so as to anchor the medical device in place.
There are primarily two methods of providing barbs on such medical devices. The first is to provide the barbs integrally with the stent or stents of the medical device. The second connects the barb or barbs to a graft element of the medical device, typically by suturing. With the first option, where the barbs are integral with a stent of the device, the barbs benefit from support of the stent and thus have enhanced rigidity and function. With this option, the barbs can either be integrally formed with the stent or fixed to the stent in a subsequent procedure. For instance, a barb may be formed by cutting a part of a stent structure to create the pin-like element of the barb. This may, for instance, be by means of laser cutting, which is a well-known method for making stents, particularly Nitinol stents. While this method provides a satisfactory barb structure fully supported by the stent, this method of manufacture is expensive. It also requires careful handling of the stent after its formation as the barb or barbs present an enhanced risk of snagging of the stent during subsequent manufacturing and handling procedures.
Another method of fixing the barb or barbs to a stent structure involves soldering or otherwise bonding the barb or barbs to the stent. This is suitable for stents made of similar materials, such as stainless steel, but is not suitable for materials which require subsequent treatment at high temperatures. For instance, barbs cannot be soldered or otherwise bonded to a Nitinol stent as such stents require subsequent heat treatment at very high temperatures (in the region of 500° C.) for shape memory setting.
With respect to the second method of coupling the barbs to a medical device, that is by suturing the barb to graft material of the device, this provides the ability to fit the barbs at a relatively late stage in the assembly or manufacture of the device. It is generally considered that such barbs should be sutured to the graft material in such a manner that the barbs cannot rub against any other hard structure of the medical device, such as any other barb or any stent of the device. Any rubbing of this nature can cause greater wear of the graft material and risks premature tear of the graft material and thus premature failure of the medical device. In addition to this, this method of attaching such barbs to the medical device involves additional and time consuming manufacturing steps.